1. Field of the Invention
This invention relates to the field of injection apparatuses used, for example, in injection molding for various applications. More particularly, the invention relates to injection nozzles used in high pressure molding of various materials at normal or elevated injection temperatures.
2. Description of the Related Art
Injection nozzles find application in a wide variety of molding machine and hot runner equipment.
U.S. Pat. No. 5,208,052 to Schmidt and U.S. Pat. No. 5,299,928 to Gellert disclose removable two-piece nozzle tips. The '052 patent discloses a removable nozzle tip made of beryllium copper having high thermal conductivity surrounded by a thermally insulating sleeve of titanium alloy, where the insulative sleeve also seals. The '928 patent discloses a similar two-piece nozzle tip made of different materials having only a different geometry. Again, one piece is of high thermal conductivity and the other piece is of low thermal conductivity, where the insulative piece also seals against plastic leaking.
U.S. Pat. No. 5,658,604 to Gellert et al. discloses a hot runner injection nozzle. The '604 patent discloses a two-piece nozzle tip where the inner portion is molded of a carbide alloy that makes it suitable for applications involving injecting of abrasive materials. This tip has a specific shape that, according to the patent, optimizes its manufacturing method. As in patent '928, a threaded sleeve made of a thermal insulation material is used to attach this carbide tip to the nozzle housing. As in patent '928, this insulation sleeve seals the mold gate to prevent leakage of molten resin.
U.S. Pat. No. 5,569,475 to Adas et al. discloses a hot runner nozzle design where a thermal insulation layer, and in some cases an additional protective layer, are applied in the areas of contact between a nozzle and a mold to limit the heat transfer. The role of the protective layer is to increase the life time of the thermal insulation layer.
However, the injection nozzle apparatuses disclosed in these patents are not suitable for high pressure injection of normal, abrasive or corrosive materials, such as various plastic resins or metals.Currently, many applications involve molding abrasive and non-abrasive materials, such as plastic resins or various metals under higher pressure (such as 50 ksi) that can be injected at either normal or at elevated temperature, such as for example up to (600-800 F). These conditions require improved injection nozzles capable of supplying molten material for quality molded parts made during longer injection runs. Preferably, the nozzles are easily removable for faster assembling and servicing. Injection nozzles for high pressure applications meeting these operational criteria in a satisfactory manner are needed. High cavitation applications impose an additional requirement, namely, a space constraint. For this reason, the diameter of the high pressure nozzles must be very small to reduce the pitch between the nozzles. This means that the components of the nozzle must have thin walls, and this limits the application of the known designs to high pressure molding.